I'm fixing up an Addams Family machine which has the WPC-089 power supply board. I measure the 12VUR and get about 10V. Normally I wouldn't care that much, but that board supplies the power to Thing's opto sensor board. Because of the low voltage, the switch inputs are constantly changing (i.e. IR LED isn't producing enough light because too little current). I jumpered the 12V regulated to the opto board, and the optos all work properly.

Here is my conundrum. I can simply lower the current limiting resistors on the opto board to 400 ohms from the factory 470 ohms, and it will work. I could also try to fix the 12VUR supply to get it closer to 12V and then I wouldn't need to switch the resistors.

The most likely issue with the 12VUR is that the bridge rectifier is old. I can replace the bridge rectifier and it might fix the problem. Next most likely culprit would be the 15mF cap that it uses to smooth the voltage out. The least likely scenario is that I lost one or two windings on the transformer, so the transformer is giving a slightly low AC voltage being fed into the bridge rectifier.

I'm not sure what else uses the 12VUR, so it may not be an issue to leave it low and just swap the resistors. If it is feeding some solenoids, it may be giving me weak kicks and that might be why the ball doesn't get to the shooter lane every time. (The machine has been sitting for years, so it also might be that it needs a general cleaning).

Which way do the pinball gods think is best? Since I'm not sure where else the 12VUR goes, I'm thinking I should start by replacing the bridge rectifier. If that voltage is just powering bulbs or other non-essential things, I would probably just replace the resistors.

What do you think I should do?

Thanks in advance for any help. Don't bother pleaing for me to sell you the machine for $100 because it is not my machine.

Yeah, I'm kind of unhappy with myself because I didn't bother checking the AC ripple last night. It was after 10 and I still had to drive home...that and the bridge wasn't socketed. With all my other machines it is socketed, so I was severely disappointed that it wasn't an easy 10 second swap it with another bridge rectifier that was working, remeasure, and swap it back.

One other piece of info that I failed to mention is that the caps look new, (or at least newer than 1992), and they have 08/06 written on them in sharpie. That makes me feel that somebody did a cap replacement job on the power supply board.

Time to eat some crow. My guess that it was the bridge rectifier (lost one of the diodes) was completely wrong. Measured the AC voltage last night and found it was 5V. It was so high that I didn't believe it and I put it on a scope. It shows that the cap is completely useless/toasted. Pat gets the thumbs up since they gave the right answer first, and iro gets another thumbs up for mentioning a meter to measure AC ripple since most people probably don't have a 'scope in their basement.

Thanks for all the help!!